True, I knew it was a bit simplistic but it was quite late. However this works on the assumption that deceleration is constant, which is highly unlikely, therefore the peak deceleration at 220 is probably a good number to use. Also if truck stops in less distance then time is reduced, so all basically a bit of a guess to get you in the right order of magnitude.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
I calculate the energy at 1.85MJ. This is very large. To put things in perspective, I design offshore oil platforms for a living and we would normally design a fixed offshore platform for about 8 times the ship impact energy as this truck impact. Only 8 times more and now compare an offshore oil platform to a puny steel gate - it is not reasonable expect a steel gate to be still working afterwards.
The design requirement is not realistic - you should be considering 2 x gates and possibly an additional barrier which can be raised out of the ground between them. A single gate is always a risk. What happens when the gate is opened for one vehicle and the terrorists waiting behind then drive through the open gate?
The difference is probably the stopping distance. Presumably you do not resolve the ship impact over 1 meter or less. Run the numbers. In the same way that it requires infinite force to reduce a centenary sag to zero, even a gnat would generate infinite force it it had to stop instantly without deformation. It becomes an issue of dividing by zero. That said, each engineer has to come to terms with what is realistic...up to a point. On issues such as this it depends who's setting the parameters and approving the design. And certain governmental authorities do indeed use the exact criteria described above for their design parameters. In short, the customers' requirements must be taken into account.
Hi
I was reading some of the post, and I wonder if any one provide a complete design for gated crash barrier
and show the detail design computations
thanks
